Clinical applicability of cone-beam computed tomography in monitoring seroma volume change during breast irradiation.

PURPOSE: To determine whether cone-beam CT (CBCT) is effective in monitoring seroma reduction during breast irradiation when compared with conventional CT.

PATIENTS AND METHODS: This study included 19 women with Stage T1-2 breast cancer treated with breast-conserving therapy. Each patient underwent two to four CT and multiple CBCT scans (mean, 8; range, 7-13 scans) at various time intervals during radiotherapy. Seroma were contoured by two observers on all scans and checked by one radiation oncologist. Seroma clarity was determined according to The British Columbia Cancer Agency Seroma Clarity Score scale, and conformity index (CI) of the two observers was evaluated. Correlations in seroma contours and seroma characteristics between CBCT and CT, as well as interobserver variation, were examined.

RESULTS: The mean differences in seroma volume between CT and CBCT (3%, p = 0.3) and between the two observers (6%, p = 0.2) were not statistically significant. Seroma clarity correlated significantly with CI for both CT and CBCT (p = 0.02 and p = 0.001, respectively), indicating the higher the seroma clarity score, the greater the CI between the observers. With seroma clarity 3 or higher for CT and CBCT, a high level of observer concordance was shown (all CI of these scans were >or=50%).

CONCLUSION: Volume discrepancy between CBCT and CT and between the two observers was not statistically significant. Seroma clarity influenced observers' ability to contour on CT or CBCT equally. Therefore, CBCT is a good clinical surrogate for CT in monitoring seroma reduction during breast radiotherapy, especially for patients with seroma clarity score 3 or higher.